It was a battle of the scientists in a Senate committee Monday over whether there is any way to determine if there is a marijuana equivalent to the blood-alcohol level used for DUIs.

After nearly seven hours of testimony, most members of Senate State, Veterans & Military Affairs Committee agreed that the science was still murky, but said there was enough to set such a level for toking while driving.

The bill passed on a bipartisan 4-1 vote amid chanting from some members of the audience, who shouted, “Shame,” at the committee.

Opponents of the measure, SB117 introduced by Sen. Steve King, R-Grand Junction, said unlike blood-alcohol levels, there was no reliable scientific way to know how much tetrahydrocannabinol in the bloodstream was too much to determine if a motorist was too stoned to drive.

“A task force last year that looked extensively at other expert witnesses from scientists, they did not come out with the same results and recommendations that Senator King presented,” said Dr. Paul Bregman, a doctor with CannaMed USA in Denver. “This is not a scientifically based bill, and needs to be further researched.”

The measure would place a zero tolerance on driving under the influence of such drugs as methamphetamine or cocaine. For marijuana, however, the bill would set a limit of 5 nanograms or more of delta 9-tetrahydrocannabinol per milliliter of whole blood.

It’s that nanogram level that drew the most debate, with some saying high THC levels don’t equate to impairment, and others saying any level of impairment is too high.

Cindy Burbach, forensic toxicologist at the Colorado Public Health and Environment, said much of the research supporters of the bill were relying on didn’t compare drug use with driving, a far more complicated task that can be impacted by drugs in unpredictable ways.

Other studies that did compare drug use and driving show clear impairment, she said.

“We are at where we should be with the science, and our colleagues have confirmed this,” she said. “Five nanograms is more than fair.”

Beyond the science, the bill pitted defense attorneys against prosecutors and law enforcement, who said the issue really is a matter of public safety.

Colorado State Public Defender Doug Wilson said DUI conviction rates are up, including in drug-related cases, while DUIs themselves are down.

Wilson said it’s already illegal to drive while under the influence of drugs, also known as DUID cases. Setting a THC level will make those marijuana-driving cases harder to prove, and be more costly for the state.

He also said there’s a reason why the Colorado Criminal and Juvenile Justice Commission isn’t backing the bill.

“You do not see support of the commission on this particular bill because of the dispute about what is the scientific evidence on impairment at the time of driving,” Wilson said. “It’s going to be court battle consistently until or unless the courts do in fact accept the science in the state.”

Thomas Raynes, executive director of the Colorado District Attorney’s Council, said setting a THC level will send a strong message to those who would use marijuana and drive, reducing marijuana-related driving arrests and accidents as a result.

“Seventeen states already have some version of zero-tolerance legislation in regard to drugs,” he said. “This is not about legal versus non-legal uses of marijuana. It’s about driving while you are impaired. It’s about being a danger to the public, and it’s about keeping those dangerous drivers off the road.”

The bill also drew dozens of other witnesses, many of whom were users of medical marijuana, who said they feared the measure would unfairly prevent them from being able to drive.

The bill heads to the Senate Appropriations Committee for more debate.